Preheat the oven to 400 degrees F.
Cook the
pancetta in a heavy large oven-safe pot over medium heat until
crisp, about 8 minutes. Add the
onions and garlic, and saute until the onions are translucent, about 5 minutes. Mix in the
beer,
tomato sauce,
brown sugar, vinegar,
molasses, mustard, salt, and pepper. Stir in the beans. Bring to a
simmer. Transfer to the oven and bake, uncovered, until the bean mixture bubbles and thickens slightly, stirring occasionally, about 45 minutes.
